This invention relates to a process for purifying lithium hexafluoroarsenate (LiAsF.sub.6) to produce a product of high purity suitable for use as an electrolyte in high energy density galvanic batteries.
The purification of LiAsF.sub.6 by recrystallization from water is inefficient due to the high solubility of the LiAsF.sub.6 in water, while purification by recrystallization from common organic solvents and mixtures thereof, e.g. acetone, dioxane, benzene, is ineffective. U.S. Pat. No. 3848063 discloses a multistep process for purifying LiAsF.sub.6 to produce a product of high purity, which includes adding the impure LiAsF.sub.6 to aqueous LiOH to cause decomposition and precipitation of impurities, adding further LiOH to maintain the pH at a minimum of 10.5 then adding HF to reduce the pH to 7.5-9.0, separating the precipitates from the LiAsF.sub.6 solution, cooling the solution to precipitate the LiAsF.sub.6 as trihydrate and dehydrating the product in vacuo. U.S. Pat. No. 3654330 also discloses a multistep process for producing a LiAsF.sub.6 product of high purity, which comprises reacting impure LiAsF.sub.6 with an excess of acetonitrile to produce the tetraacetonitrilolithium salt Li(CH.sub.3 CN).sub.4 AsF.sub.6, removing the excess acetonitrile, and heating the salt in vacuo to decompose the salt and remove the acetonitrile and thereby produce a LiAsF.sub.6 of exceptionally high purity.